Torque limiting apparatus



A ril 25, 1967 J, K. HOLDO ETAL 3,315,754

TORQUE LIMITING APPARATUS Filed Nov. 18, 1964 Armmw United States Patent3,315,754 TORQUE LTMETING APPARATU Jan Kristian Hoido, Stockholm, andBengt Arvid Westerinnd, Klinten, Sweden, assignors to Atlas CopcoAktiebolag, Nacka, Sweden, a corporation of Sweden Filed Nov. 18, 1964,Ser. No. 412,023 16 Claims. (Cl. 173-12) This invention relatesgenerally to torque limiting apparatus for limiting the maximum torquetransmitted from a rotary driving motor to an element rotated by themotor. More specifically the invention relates to torque limitingapparatus applicable to power wrenches of the rotary as well as of theimpacting type.

In many technical applications, such as for example in tightening downthreaded fasteners during assembly of machine or structural elements,control of the final torque applied to the fasteners is important forthe provision of uniform tightening and maximum strength in theconnection. Normally the rotated element such as the tool shaft or headof a power Wrench, rotates rapidly at the beginning of the tighteningoperation but then slows down gradually with increased resistance torotation until the drive is interrupted when the desired final torquehas been reached. Similarly in power wrenches of the impacting type thetool head together with the fastener during the continuously repeatedblows turns a certain angle for each blow and this angle decreasessuccessively from blow to blow with increasing tightness. In rotary aswell as impact tightening the angle of displacement per unit of time ofthe tool shaft, tool head or fastener thus evidently is a measure forthe torque applied to the fastener and can be used for purposes oflimiting the final torque to a predetermined value.

It is an object of the invention to provide a simple and eflicienttorque limiting apparatus for controlling the final or maximum torquetransmitted from a driving motor to an element rotated thereby whichapparatus measures the angular displacement per unit of time of therotated element and cuts off the supply of power to the motor when theangular displacement per unit of time has decreased to a predeterminedvalue. A further object of the invention is to provide a torque limitingapparatus of the above character in which the measuring is performedcontinuously by pneumatic means and the cut off of power is controlledby means responsive to the behaviour of the pneumatic measuring means.

The above and other objects of the invention will become obvious fromthe following description and from the accompanying drawings in whichtwo embodiments of the invention are illustrated by way of example. Itshould be understood that these embodiments are only illustrative of theinvention and that various modifications may be made within the scope ofthe claims without departing from the scope of the invention.

In the drawings FIG. 1 is a longitudinal sectional view through a powerwrench incorporating the apparatus according to the invention; FIG. 2ais a sectional view on the line 22 in FIG. 1; FIG. 2b is a sectionalview through a modified embodiment of the automatic control valveforming part of the wrench shown in FIG. 1; FIG. 2c is a measuringinstrument coupled to a line connecting the elements shown in FIGS. 2::and 2b; FIG. 3 shows a sectional view on the line 33 in FIG. 1.

In the figures the numeral designates a rotary pressure fluid drivenpower wrench which may be of any suitable conventional type with orwithout impact action. For purposes of illustration has been chosen animpact wrench similar to the one disclosed in US. patent applicationSer. No. 184,013, now Patent No. 3,179,219 to Kardn but the invention isnot restricted to power wrenches of that particular type. Accordingly,there is provided in the housing 11 of the power wrench 10 a reversiblerotary air motor 12 having radial driving vanes 13 on a rotor 14, therotational direction of which is controlled by the usual reversing valve15. The reversing valve 15 and motor 12 are supplied with compressed airthrough a passage 16 controlled by a control valve 17 which can beoperated manually by a trigger 18 on the handle 19 of the power wrench10. An air-nipple 20 upstream of the control valve 17 receivescompressed air from a supply hose, not shown, connected thereto. Therotor 14 of the air motor 12 is coupled for rotating a hammer 21journalled in the housing 11. The hammer 21 is supported at its rear endon a splined projection of the rotor 14 while its forward end slides onthe tool shaft or anvil 22 of the power wrench. The rear end of theshaft 22 is supported inside of the hammer 21 While its middle portionis journalled in the front end of the housing 11. The outer end of theshaft 22 has the usual square end 23 for removably carrying toolsengageable with the fasteners to be driven. As described in full detailin the above-mentioned patent an impact dog 24 pivotally journalledinside of the hammer 21 delivers impacts to the shaft 22 when the lattermeets sufiicient resistance to rotation. The impact dog 24 is moved toimpact delivering position. FIG. 3, by a cam 25 on the shaft 22cooperating with the trailing edge of the impact dog 24, while a torsionspring 26 extending centrally and longitudinally of the Wrench 10, inthe position depicted in FIG. 3 cooperates with a pin 49 on the impactdog 24 so that the leading edge thereof is pivoted out of engagementwith the shaft 22 and the impact dog 24 will be able to rotate in unisonwith the hammer 21 around the arrested shaft 22 for producing the nextimpact.

The apparatus for limiting the application of torque to the fastenersdriven by the power wrench 10 includes an automatic control valve 27 ina valve case 31 upstream of the manual control valve 17. The valve 27 isa fiat disk valve cooperating with a circular valve seat 28 in thepassageway 29 connecting the nipple 20 with the manual control valve 17.The automatic control valve 27 has a projecting piston end 3!} which isslidably but tightly received in a bore in the valve case 31 whereby thecontrol valve 27 is guided in its movements between a cut-off and anopen position. Adjacent the piston end 36 in the valve case 31 there isprovided an air chamber or reservoir 32 in which one end of a helicalspring 33 bears against the face of the piston end 30. The opposite endof the spring 33 is supported by a washer 34, the axial position ofwhich in the chamber 32 can be adjusted by means of a set screw 35,which extends through the wall of the valve case 31 and is in threadedengagement therewith. From the passageway 29 a branch passage 36 leadsto the chamber 32. The air flow through the passage 36 can be controlledby a needle valve 37.

The chamber 32 is connected to the forward end of the power wrench 10 bya conduit 38 communicating with a bore 39 disposed preferablyperpendicularly to the surface of the shaft 22. The bore 3? is providedin a fitting 4t), FIG. 2a, connected to the housing 11 as by screws 41.A nozzle body 42 is slidable in the bore 39 and has an O-ringtherearound for providing tightness between the nozzle 42 and the bore39. The nozzle 42 is preferably made of plastic material offering smallfrictional resistance to sliding motion against metal and sliding incollector brush manner on the periphery of the shaft 22. A bore 43extends axially through the nozzle 42. A helical spring 44 is interposedbetween a shoulder in the bore 39 and the nozzle 42 for urging thelatter against the shaft 22.

A series of axial grooves 45 are provided in evenly spaced dispositioncircumferentially on the shaft 22 and 3 the portion thereof forming thepath of movement of the nozzle 42 during rotation of the shaft 22.Between the grooves 45 peripheral boom portions 46 of the shaft 22remain undisturbed.

The passage 16 upstream of the reversing valve 15 is connected by aconduit 50 to the chamber 32 in the valve case 31. A spring pressedcheck valve 51 opening for flow in the direction from the chamber 32 tothe passageway 16 is provided in the conduit 50 and the valve case 31.

A bleed hole 52 is provided in the valve disk of the automatic controlvalve 27 whereby air can bleed past the valve 27 in the cut-off positionthereof.

In operation let it be assumed that the fastener to be driven is rotatedby the air motor 13 over the rotor 14, the hammer 21, the impact dog 24,the shaft 22, the square end 23 and a tool, not shown, carried thereby.Compressed air is delivered to the nipple 20 past the seat 28 of theautomatic control valve 27 in the open position thereof and past themanual control valve 17 to the passageway 15 and on to the reversingvalve 15 and the motor 12 for rotating the vanes 13 thereof.Simultaneously herewith a certain quantity of air is branched from thepassageway 29 via the branch passage 36 and the needle valve 37 to thechamber 32 and thence via the conduit 38 to the bore 43 of the nozzle42.

During initial rotation of the shaft 22 as well as during the firstrapidly repeated impacts of the hammer 21 and dog 24 against the shaft22, the grooves 45 thereon will pass the bore 4-3 with a high angularvelocity and with the needle valve 37 set at a lesser flow rate thanissuing from the bore 43, no pressure rise will occur in the chamber 32since the grooves 45 passing the nozzle 42 in rapid succession obviouslyact to keep the bore 43 substantially open to atmosphere. However, withincreasing resistance to rotation of the fastener, that is to say withincreasing torque, the angle of displacement produced by each separateimpact successively decreases. With the hammer 21 normally delivering asubstantially constant number of impacts per time unit this obviouslymeans that the total angular displacement per unit of time of the shaftlikewise decreases. Thus the boom portions 46 on the shaft 22 betweenthe grooves 45 will take a longer time to pass the bore 43, therebyoffering a successively increasing obstruction to the flow therethroughwith increased torque. This obstruction causes a rise of pressure in thechamber 32, whereby a force tending to close the automatic control valve27 is imposed on the face of the piston end 30. This force is added tothe force exerted by the helical spring 33 but both these forces arecounteracted by the pressure acting on the valve 27 in the passageway29. By adjustment of the set screw 35 and of the needle valve 37 thespring force and the air flow branched to the chamber 32 are set to suchvalues that the automatic valve will be moved to the cutoff position bythe pressure built up in the chamber 32 at the right momentcorresponding to the desired torque in the fastener.

The valve disk of the automatic control valve 27 is disposed at arelatively small distance from the seat 28 in the open position of thevalve 27 in such manner as to create a pressure differential across thevalve disk assisting in closing the valve 27 at the desired instant witha snap action. The compressed air trapped in the passage 16 expands uponclosing of the automatic valve 27 through the air motor 12. The fallingpressure in the passage 16 results in that the check valve 51 in theconduit 50 is opened whereupon the chamber 32 is exhausted to atmospherevia the motor 12. As long as the operator keeps the trigger 18 depressedand the manual control valve 17 is open, air leaking from the passageway29 through the bleed hole 52 in the valve 27 will likewise leak out toatmosphere through the passage 16 and the motor 12 so that the automaticcontrol valve 27 will remain closed. If the trigger 18 is released,whereby the valve 17 is closed, the air issuing through bleed hole 52will rapidly equalize the pressures at opposite sides of the valve diskof the valve 27, whereupon the pressure in the passageway 29 will returnthe valve 27 to open position against the action of the spring 33. Thechamber 32 is exhausted to the atmosphere by the conduit 50 and themotor 12 or by the conduit 38 when one of the grooves 45 registers withthe bore 43 in the nozzle 42. The opening force acting on the valve 27is therefore not counteracted by pressure in the chamber 32. The powerwrench It) is thus again in starting position and ready for the nexttightening cycle.

In the above described operation limiting of the torque was performedduring impact action of the power wrench. The present apparatus is,however, equally suited for limiting the torque also during purelyrotary action of the wrench to which the apparatus is applied. In FIG.1, for example, by suitably releasing the set screw 35 and by adjustingthe needle valve 37 to suitably increase the flow area of the passage36, torque limiting will be possible during rotation, provided theinternal driving friction between the hammer 21, the dog 24 and theshaft 22 is sufficiently high to allow transmission of torque withincertain limits without impacting taking place. With increased resistancethe rotation will slow down gradually and the decrease in the number ofgrooves 45 passing the bore 43 per unit of time will cause pressure tobuild up in the chamber 32 until the automatic control valve 27 isclosed at the pressure value in the chamber 32 corresponding to thedesired torque. The operation will be identical when the presentapparatus is applied to rotary power wrenches of other type.

The modified automatic control valve shown in FIG. 2b has an axialcentral passage 53 through the piston end 30 and through a tubularextension 54 coaxially thereon. The extension 54 is tightly but slidablyreceived in a partition 55 forming the rear wall of the air chamber 32in the valve case 56. Through a nipple 57 screwed to the valve case 56and disposed coaxially with the automatic valve 27 compressed air entersfrom the supply hose, not shown, and passes along the central passage 53through radial apertures 58 to the rear of the valve disk included inthe automatic valve 27. The bleed hole 52 is in this instance providedcentrally in the valve disk. The action of the automatic valve 27depicted in FIG. 2b is identical with the operation of the valve in FIG.1 except for the compressed air being supplied axially through the valve27 past the chamber 32. The helical spring 33 bears against thepartition 55 and cannot be adjusted since no set screw is providedtherefor. As before a needle valve 37 provides a means for adjusting thedesired maximum torque at which the power to the tool is to be cut off.

A pressure gauge 59 may be connected to the conduit 38 wherebyadjustment of the torque limiting apparatus is made more easy when usingthe spring 33 for pressure adjustments. The gauge 59 can also be usedfor indicating the moment at which the operator has to interrupt thesupply of power purely manually for reaching the desired value of thefinal torque. However, such manual control, during which the automaticvalve 27 can be omitted or made inoperative, depends heavily upon theskill of the operator and is undesirable in production work. Furthermorethe pressure gauge 59 obviously can be used as an indicator of theangular velocity of the shaft 22. In such case the disk of the automaticvalve 27, FIG. 2b, will be omitted so that driving air constantly canpass to the driving motor of a rotary shaft 22 arranged as indicated inFIG. 2a. By the aid of a tachometer the readings on the gauge 59 can becalibrated to indicate the angular velocity of the shaft 22 whereby thedevice according to FIGS. 2a-2c can be used for direct measurement ofangular velocity.

What we claim is:

1. A torque limiting apparatus comprising in combination a rotary motor,a member connected to said motor for being rotated thereby, means formeasuring the angular displacement per unit of time of said member, andautomatic means for cutting of the supply of power to said motor, saidmeasuring means operative upon the decrease of said angular displacementper unit of time to a predetermined value to cause actuation of saidautomatic mfieans whereby the supply of power to said motor is cut 0 2.In an apparatus for limiting the maximum torque transmitted from acompressed air driven motor to an element rotated thereby thecombination which comprises said motor and element, an air lineconnected to said motor for supplying compressed air thereto, a driveshaft connected between said motor and element, pneumatic measuringmeans cooperating with said shaft in a manner to build up a pressure insaid means which inrreases with decreasing angular displacement per unitof time of said shaft, a valve in said air line for cutting off the airsupply to said motor, and means connected to said valve and operativeupon the development of a predetermined pressure in said measuring meansto cause actuation of said valve whereby the supply of air to said motoris cut off.

5. A power wrench comprising a housing, a rotary motor in said housing,a tool head connected to said motor for being rotated thereby andprotruding from said housing, a shaft included in said tool head, aseries of axial grooves in evenly spaced disposition circumferentiallyon said shaft, a nozzle nonrotatably supported in said housing andhaving an outlet orifice adjacent the periphery of said shaft andtraversing said grooves and the portions of said shaft therebetweenduring rotation of said tool head, said portions obstructing flowthrough said orifice when in registry therewith, a passagewaycommunicating with said nozzle and orifice, means for constantlysupplying air under pressure to said passageway at a lesser rate thanissuing through said orifice when said orifice registers with saidgrooves, and automatic means responsive to the development of apredetermined pressure in said passageway as a result of the obstructionoffered by said portions during rotation of said tool head and shaft forautomatically cutting ofl. the supply of power to said motor.

4. A power wrench as set forth in claim 3 in which said nozzle isaxially slidably supported in said housing and in which there areprovided means for biasing the end of said nozzle carrying said orificeinto sliding contact with said shaft and said portions thereon.

5. A power wrench as set forth in claim 3 in which there is provided anadjustable valve in said air supply means for adjustably controlling theair supply to said passageway.

6. A portable pneumatic power wrench comprising a rotary air motor, ashaft driven by said motor, a first passageway for supplying said motorwith air under pressure for rotating said shaft, a valve seat in saidfirst passageway, an automatic control valve in said first passagewayupstream of said seat and movable between open and seated positions toadmit or cut off the supply to said motor, resilient means urging saidvalve to seated position, a first surface on said valve exposed topressure in said first passageway for maintaining said automatic valvein open position against the action of said resilient means, a secondpassageway branched ofi from said first passageway at a point upstreamof said valve seat, a second surface on said valve opposed to said firstsurface and communicating with said second passageway, said secondsurface responsive to the development of a predetermined pressure insaid second passageway for combining its action with the action of saidresilient means to move said valve to seated position, and pneumaticmeans connected to said second passageway and receiving air underpressure therefrom, said pneumatic means being responsive to decrease ofthe angular displacement per unit of time of said shaft to apredetermined value for developing said predetermined pressure in saidsecond passageway in order 6 to move said automatic valve to seatedposition and thereby to stop said motor.

'7. A power wrench as set forth in claim 6 in which said automatic valvein the open position thereof is disposed in such proximity to said seatas to create a pressure differential across said valve for placing anadditional bias on said valve towards said seated position thereofduring operation of said motor.

8. A power wrench as set forth in claim 6 having a manually operablecontrol valve in said first passageway downstream of said seat, saidcontrol valve being movable between open and closed positions to admitor cut off the air supply to said motor, there being provided a bleedpassage in parallel with said automatic valve in the closed positionthereof for pressure equalization at opposite sides of said seat and forresetting said automatic valve to open position when said manuallyoperable valve is closed.

9'. A power wrench as set forth in claim 8 including a communication forconnecting said second passageway with said first passageway at a pointbetween said control valve and said motor, and a check valve in saidcommunication for relieving the pressure in said second passageway whensaid manually operable valve is closed.

16'. A power wrench as set forth in claim 6 in which there are providedmeans for adjusting the bias of said resilient means exerted upon saidautomatic valve.

11. An impact wrench comprising a housing, a rotary air motor in saidhousing, a rotatable hammer in said housing connected to said motor, ananvil shaft rotatably journalled in said housing and carrying a toolhead at one end thereof, said tool head protruding from said housing andhaving means thereon connectable to a threaded fastener to be driven,means for transmitting rotational blows from said hammer to said anvilshaft in response to said shaft meeting sufficient resistance torotation of said fastener, said blows causing successively decreasingangular displacements of said anvil shaft with increasing resistance ofsaid fastener, a passageway for supplying air under pressure to saidmotor for operating the same, an automatic valve controlling saidpassageway and movable between open and closed positions to admit or cutofi the supply of air to said motor, and means responsive to the angulardisplacements per unit of time of said anvil shaft decreasing to apredetermined value for effecting the movement of said valve to closedposition to stop said motor.

22. An impact wrench as set forth in claim 11 comprising a series ofaxial grooves in evenly spaced disposition circumferentially on saidshaft, a nozzle nonrotatably su ported in said housing and having anoutlet orifice adjacent said shaft for traversing said grooves and theportions of said shaft therebetween as a consequence of said angulardisplacements, said portions being in such proximity to said nozzle whenin. registry therewith as to obstruct flow through said orifice, asecond passageway communicating with said nozzle and orifice, means forsupplying air under pressure to said second passageway at a lesser ratethan issuing through said orifice when said orifice registers with saidgrooves, and means responsive to the development of a predeterminedpressure in said second passageway as a result of the obstructionoffered by said portions during consecutive angular displacements ofsaid shaft for effecting the movement of said valve to closed positionto stop said motor.

13. An impact wrench as set forth in claim 12 in which said secondpassageway is branched ofi? from said first passageway upstream of saidautomatic valve and said means for supplying air to said secondpassageway is an adjustable valve.

14. An impact wrench as set forth in claim 12 in which said secondpassageway includes an air reservoir chamber.

15. A device for measuring the angular velocity of a shaft rotated bypower comprising a rotary shaft, a series of grooves in evenly spaceddisposition circumferentially on said shaft, a nozzle non-rotatahlysupported adjacent said shaft and having an outlet orifice supported totraverse said grooves and the portions of said shaft therebetween duringrotation of said shaft, said portions obstructing flow through saidorifice when in registry therewith, a passageway communicating with saidnozzle and orifice, means for constantly supplying fluid under pressureto said passageway at a lesser rate than issuing through said orificewhen said orifices register with said grooves, and a pressure gaugeconnected to said passageway to respond to pressure fluctuations thereinthereby to indicate the angular velocity of said shaft and itsfluctuations with rotational resistance.

16. A measuring device as set forth in claim 15 in which said nozzle isaxially slidably supported in said housing and in which there areprovided means for bias- 8 ing the end of said nozzle carrying saidorifice into sliding contact with said shaft and said portions thereon.

References fitted by the Examiner UNITED STATES PATENTS 3,136,326 9/1964Bryant 7352l 3,195,655 7/1965 Karden 17312 3,216,252 11/1965 Chapmen etal 73521 PQREIGN PATENTS 1,104,233 4/1961 Germany.

1,176,405 8/1964 Germany.

FRED C. MATTERN, In, Primary Examiner.

L. P. KESSLER, Assistant Examiner.

1. A TORQUE LIMITING APPARATUS COMPRISING IN COMBINATION A ROTARY MOTOR, A MEMBER CONNECTED TO SAID MOTOR FOR BEING ROTATED THEREBY, MEANS FOR MEASURING THE ANGULAR DISPLACEMENT PER UNIT OF TIME OF SAID MEMBER, AND AUTOMATIC MEANS FOR CUTTING OF THE SUPPLY OF POWER TO SAID MOTOR, SAID MEASURING MEANS OPERATIVE UPON THE DECREASE OF SAID ANGULAR DISPLACEMENT PER UNIT OF TIME TO A PREDETERMINED VALUE TO CAUSE ACTUATION OF SAID AUTOMATIC MEANS WHEREBY THE SUPPLY OF POWER TO SAID MOTOR IS CUT OFF. 